Controlling Excel Add-ins and Microsoft Store App Installations

We have a requirement to block users from adding add-ins to Excel and Installing certain application directly which utilize Microsoft Store apps. Below are the two scenarios we need to address. I would appreciate any guidance or recommendations on how to implement these controls.

1) Blocking Excel Add-ins from Microsoft Store

Users are currently able to add add-ins such as “Claude by Anthropic in Excel” directly from the Microsoft Store apps. For example, if a user accesses the URL: https://marketplace.microsoft.com/en-us/product/saas/wa200009404?tab=overview they can proceed to add the add-in to Excel.

So, We need a method to prevent users from adding Office add-ins from the Microsoft Marketplace or external sources.

2) Blocking Installation of Microsoft Store Apps (e.g., WhatsApp)

We are currently blocking Microsoft Store apps on OS level. However, users can still download and install applications such as WhatsApp directly from the vendor website, which utilize Microsoft store apps in backend: https://www.whatsapp.com/download

We are considering configuring the Intune policy “Only Private Store is enabled.” However, we noticed that enabling this setting prevents users from accessing certain built-in applications (e.g., Notepad). Is there any other way to block access Microsoft Store apps directly? 

Thank you in advance for your assistance.

Dilan